The disclosure relates generally to components having cooling passages cast therein, for high temperature environment use in turbomachines. More particularly, the disclosure relates to a static core tie rod for securing the position of a core during the casting operation and plugging the core tie hole in the wall of the cooling passageway of the component.
Components in turbomachines such as gas turbines typically operate in high temperature environments. In order to efficiently cool components in the hot gas path, such as nozzles and buckets, cooling passageways may be cast into the bodies of the components during fabrication. These cooling passageways allow a fluid to circulate through the cooling passageways, carrying heat away from the component.
In a casting process used to manufacture components having cooling passageways therein, cores made of, e.g., ceramic, may be positioned inside a mold. Small rods called core ties may be embedded in the cores to provide rigidity to the core structure and positively locate the cores in the three-dimensional space within the mold, with respect to the mold, to other cores, and to other legs of the same core. The core ties may be made of a variety of materials including, e.g., ceramic materials, alumina, quartz, or metal alloys.
After casting, the cores and the core ties are typically leached out of the body of the component, leaving behind cooling passageways where the cores had been. Due in part to differences in material composition, core ties may be more difficult and more expensive to leach out than the ceramic cores. In particular, additional leaching cycles and different/higher temperatures may be required in order to remove the core ties. When the core ties are removed, holes remain in the walls of the cooling passageways where the core ties had been. These holes in the cooling passageway walls require additional processing to be sealed by, e.g., welding, brazing, threading, or other means, such as inserting a plug into or over the hole.